A thread delivery device of this type is known from German Patent Specification No. 1,903,133. It has the advantage that, as a result of the intermediate thread supply being wound in the form of a multilayer irregularly wound ball of thread on to a device of predetermined size, a substantially larger intermediate thread supply can be stored than when thread is stored in a single layer, which was hitherto the only method in use. The known device has proved the most successful in practice; in particular, the thread running off may be detached from the ball of thread without pulling occurring.
German Auslegeschrift No. 1,760,600 discloses a thread delivery device providing a thread control element which is movable into the path of the thread running off the drum and limits the relative rotation of the withdrawn thread about the storage drum, thus preventing the withdrawal speed of the thread from exceeding its wind-on speed. A positive thread feed is achieved in this way despite the thread being withdrawn overend from the drum. The latter type of apparatus also operates satisfactorily if the intermediate thread supply is wound on to its storage drum in the form of a multilayer ball of thread. However, there are certain qualities of thread in which there is a very great degree of adhesion between adjacent thread windings. This occurs for example when the thread is a mixed yarn consisting of different long, loose and strong fibres. In such cases it occasionally happens that the final winding in front of the braking device, i.e. the next winding to be drawn off, tears the following winding and sometimes even another winding, thereby causing an abrupt drop in tension.
The problem underlying the invention is, in the case of a thread delivery device of the initially described type, to ensure that two or more windings are not wound off the storage drum simultaneously during positive thread delivery, also when closely adhering yarns are processed.
This problem is solved in accordance with the invention in that, when there is a positive thread feed in which the thread running off the storage drum engages on a lateral thread control element in a manner known per se, which control element limits the thread unwinding speed to the thread wind-on speed, the last thread winding which is situated directly in front of the braking device and is the next winding to be drawn off the storage drum is guided by the drum via a thread guide element, radially spaced from the drum and fixed relative to the thread control element, and guided back thereby to form a partial winding on the storage drum.
In the thread delivery device according to the invention the last thread winding slightly in front of the unwinding station forms a loop around the thread guide element. In this way the thread only comes into contact with part of the circumference of the storage drum. The area of contact between the final thread winding and the previous winding is greatly reduced thereby and it can no longer happen that the final thread winding tears the previous windings adjacent thereto.
In a thread delivery device in which the storage drum is rotatable and the thread control element is mounted on a support arm extending outside the storage drum parallel to the drum axis, such as shown in U.S. Pat. No. 3,908,921, it is advantageous if the final thread winding is wound round the support arm. As a result of this, additional structural components are not required to separate the final thread winding partially from the adjacent windings.
In a thread delivery device in which the storage drum is fixed and the thread control element mounted on a rotatable thread winding element, as also shown in U.S. Pat. No. 3,908,921, the thread guide element is preferably in the form of a guide rod projecting from the thread winding element parallel to the drum axis.
The thread control and guide elements advantageously have little or no angular spacing relative to the storage drum axis. This ensures that the final thread winding still has a sufficient degree of winding.
The surface of the thread guide element which is in contact with the last thread winding is preferably designed to be low in friction. When the storage drum or winding element rotates, the final thread winding runs over and beyond the surface of the thread guide element so that friction must be kept particularly low at this point.